Two scientists from the University of Washington studied 15 years of climate data to confirm their suspicions about how the moon influences rainfall on Earth.

By Story Hinckley

When the moon is directly overhead, less rain falls, scientists from the University of Washington (UW) recently discovered.

UW doctoral student in atmospheric sciences Tsubasa Kohyama suspected there might be a correlation between atmospheric waves and oscillating air pressure. To confirm his suspicions, Kohyama and his atmospheric sciences professor John Wallace began studying years of data.

And 15 years of data from 1998 to 2012 collected by NASA and the Japan Aerospace Exploration Agency’s Tropical Rainfall Measuring Mission (TRMM) confirmed the scientists’ assumption: Earth’s rainfall is connected to the moon.

“When the moon is overhead or underfoot, the air pressure is higher,” Kohyama explained in a statement, allowing for more moisture. “It’s like the container becomes larger at higher pressure.”

In other words, when the moon is high overhead – or at its peak – its gravitational pull causes the Earth’s atmosphere to bulge towards it, simultaneously increasing atmospheric pressure. Higher pressure increases air temperature, and warmer air can hold more moisture, making it less likely to dump its moisture contents.

An earlier study by Kohyama and Wallace published in 2014 confirmed that air pressure on the Earth surface rose higher during certain phases of the moon, specifically when it was directly overhead or underfoot.

But the recent study published Saturday in Geophysical Research Letters is the first of its kind.

“As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall,” Kohyama, a UM doctoral student in atmospheric sciences, said in a statement.

But the recent discovery may only be relevant to academics in the field because the average person will not notice a difference. The change in rainfall from lunar influence is roughly one percent of total rainfall variation, hardly enough to warrant attention.

“No one should carry an umbrella just because the moon is rising,” Kohyama tells Tech Times.

But atmospheric scientists can use the data to test climate models, says Wallace.

The study also proves the importance of the TRMM collaboration, because without its 15 years of data Kohyama and Wallace’s discovery would have been impossible. Launched in November 1997 and expected to last only three years, the TRMM satellite continues to produce valuable atmospheric data each year.

And while the change may be small, the authors say the moon’s position directly correlates with precipitation levels.

“The analysis of the relationship between relative humidity and [changes in precipitation rate] serves as a concrete illustration of how the quantitative documentation of the observed structure of atmospheric tides can be used to make inferences about atmospheric processes,” the authors explain in their paper.

Wallace says he plans to continue studying the relationship between rainfall and the moon. Next, he wants to see if there is specifically a lunar connection between certain categories of rain like torrential downpours.

There is no precedent in contemporary weather records for the kinds of droughts the country’s West will face, if greenhouse gas emissions stay on course, a NASA study said.

No precedent even in the past 1,000 years.

The feared droughts would cover most of the western half of the United States — the Central Plains and the Southwest.

Those regions have suffered severe drought in recent years. But it doesn’t compare in the slightest to the ‘megadroughts’ likely to hit them before the century is over due to global warming.
These will be epochal, worthy of a chapter in Earth’s natural history.

Even if emissions drop moderately, droughts in those regions will get much worse than they are now, NASA said.

The space agency’s study conjures visions of the sun scorching cracked earth that is baked dry of moisture for feet below the surface, across vast landscapes, for decades. Great lake reservoirs could dwindle to ponds, leaving cities to ration water to residents who haven’t fled east.

“Our projections for what we are seeing is that, with climate change, many of these types of droughts will likely last for 20, 30, even 40 years,” said NASA climate scientist Ben Cook.

It lasted about 10 years. Though long, it was within the framework of a contemporary natural drought.

To find something almost as extreme as what looms, one must go back to Medieval times.

Nestled in the shade of Southwestern mountain rock, earthen Ancestral Pueblo housing offers a foreshadowing. The tight, lively villages emptied out in the 13th century’s Great Drought that lasted more than 30 years.

No water. No crops. Starvation drove populations out to the east and south.

If NASA’s worst case scenario plays out, what’s to come could be worse.

Its computations are based on greenhouse gas emissions continuing on their current course. And they produce an 80% chance of at least one drought that could last for decades.

One “even exceeding the duration of the long term intense ‘megadroughts’ that characterized the really arid time period known as the Medieval Climate Anomaly,” Cook said.

That was a period of heightened global temperatures that lasted from about 1100 to 1300 — when those Ancestral Pueblos dispersed. Global average temperatures are already higher now than they were then, the study said.

The NASA team’s study was very data heavy.

It examined past wet and dry periods using tree rings going back 1,000 years and compared them with soil moisture from 17 climate models, NASA said in the study published in Science Advances.

Scientists used super computers to calculate the models forward along the lines of human induced global warming scenarios. The models all showed a much drier planet.

Some Southwestern areas that are currently drought-stricken are filling up with more people, creating more demand for water while reservoirs are already strained.